1. Field of the Invention
The invention relates to an AC power supply and a method for dynamically controlling the output current thereof. In particular, the invention relates to a current control method for suppressing the DC current injection and even harmonic in the output current.
2. Description of Related Art
For an AC power supply, the harmonic and the DC current injection inside its output current have to be suppressed. One suppressing method is to use an isolating transformer. However, the drawback is that the isolating transformer will result in some power loss for the AC power supply. Since the isolating transformer is an additional device, it will increase the cost and the volume of the AC power supply.
Another method is shown in FIG. 15, as also disclosed in a German patent, DE 10,249,122. That method can suppress the DC current injection as well. An additional capacitor (Cm) is used as a current detector. According to detecting the voltage across both ends of the capacitor (Cm), an output current feedback signal can be obtained. However, the output current will result in a voltage drop on the capacitor (Cm) due to the charge accumulation effect. To reduce the detection voltage of the capacitor, the capacitor itself has to be a large-capacitance AC capacitor. In that case, the cost and volume are the drawbacks of the AC power supply.